In chemistry and manufacturing, electrolysis is a method of using direct electrical current (DC) to drive an otherwise non-spontaneous chemical reaction. Electropolishing is an application of electrolysis for deburring metal parts and for producing a bright smooth surface finish.
The substrate or article to be electropolished is immersed in a bath of electrolyte solution and subjected to a direct electrical current. The substrate is the anode connection and one or more metal conductors surrounding the substrate in the electrolyte solution form the cathode connection.
Electropolishing relies on two opposing reactions that control the process. The first of the reactions is a dissolution reaction during which the metal from the surface of the substrate passes into solution in the form of ions. Metal is thus removed ion by ion from the surface of the substrate.
The other reaction is an oxidation reaction during which an oxide layer forms on the surface of the substrate. Buildup of the oxide film limits the progress of the ion removal reaction. This film is thickest over micro depressions and thinnest over micro projections. Because the electrical resistance is proportional to the thickness of the oxide film, the rate of metallic dissolution is fastest at the micro projections and slowest at the micro depressions. Thus, electropolishing selectively removes microscopic high points or “peaks” faster than the rate of attack on the corresponding micro depressions or “valleys.”
Although conventional electropolishing has proven successful in many ways, it still has some drawbacks. For example, conventional electropolishing methods and electrolyte solutions often cannot produce substrates having a high specular finish. Also, conventional electropolishing processes for producing high gloss substrates tend to operate inefficiently at relatively high temperatures, using longer polishing times, and relatively high energy requirements.